Visualizing synaptic plasticity in vivo by large-scale imaging of endogenous AMPA receptors

Abstract

Elucidating how synaptic molecules such as AMPA receptors mediate neuronal communication is crucial to understanding cognition and disease, but current technological barriers preclude large-scale exploration of molecular dynamics in vivo. We have developed a suite of innovative methodologies that break through these barriers: a transgenic mouse line with fluorescently tagged endogenous AMPA receptors, two-photon imaging of hundreds of thousands of labeled synapses in behaving mice, and machine-learning-based automatic synapse detection. Using these tools, we can longitudinally track how the strength of individual synapses changes during behavior. We used this approach to generate an unprecedentedly detailed spatiotemporal map of synaptic plasticity underlying sensory experience. More generally, these tools can be used as an optical probe capable of measuring functional synapse strength across entire brain areas during any behavioral paradigm, describing complex system-wide changes with molecular precision.

Cross-modality supervised image restoration enables nanoscale tracking of synaptic plasticity in living mice

“…Preserving the intensity and size of SEP-labelled synapses is critical to provide an accurate assessment of AMPAR changes at these sites, as SEP fluorescence is directly correlated with synaptic strength (Graves et al, 2021). To assess how image restoration impacts the distribution of synapse shape, intensity, and spatial distribution throughout the brain, we generated validation data with paired high-resolution volumes, imaged with Airyscan microscopy ( Slice Airy) , and low-resolution volumes, imaged with 2p excitation and resonance scanning ( Slice 2p , Fig 2a-b ).…”

“…This visualization is possible as the acidity of the internal cellular environment quenches the fluorescence of non-functional internalized receptors, whereas the functional complement of receptors fluoresce at neutral pH at the cell surface. Observing SEP-labeled AMPAR fluorescence in vivo has recently been used to track changes in synaptic strength in living animals (Chen et al, 2021; Graves et al, 2021; Roth et al, 2020; Tan et al, 2020; Zhang et al, 2015). Using a transgenic approach that fluorescently labels all endogenous synaptic proteins in a manner that minimizes disruptions to native protein expression and does not impair physiological function (Graves et al, 2021).…”

“…Observing SEP-labeled AMPAR fluorescence in vivo has recently been used to track changes in synaptic strength in living animals (Chen et al, 2021; Graves et al, 2021; Roth et al, 2020; Tan et al, 2020; Zhang et al, 2015). Using a transgenic approach that fluorescently labels all endogenous synaptic proteins in a manner that minimizes disruptions to native protein expression and does not impair physiological function (Graves et al, 2021). Thus while it is now theoretically possible to comprehensively visualize all synapses in living mice to create an intricate and dynamic map of synaptic plasticity across the entire brain, significant technical barriers remain to be overcome in analyzing such imaging data.…”

From Neurons to Cognition: Technologies for Precise Recording of Neural Activity Underlying Behavior

“…Moreover, to understand the guiding principles of how neural activity patterns are formed, we will need to advance technologies to study the cellular and molecular mechanisms underlying neuronal plasticity in live animals. Recent advances in in vivo imaging of intracellular signaling [57][58][59], neuronal structure [198], and synaptic proteins [199,200] as well as superresolution imaging in vivo [201] have demonstrated the potential for this field and will need to be combined with neuronal activity recordings in the future.…”

Flexible cognition in context-modulated reservoir networks

“…For example, how does synaptic plasticity support our ability to learn new tasks? While Hebb first proposed the link between synaptic plasticity and learning over 70 years ago [8], only recently have technically innovative studies documented how specific synaptic connections are altered for specific tasks [9][10][11][12][13]. But despite these new (yet sparse) experimental results, it is still not clear how widely synaptic plasticity occurs, and during what kinds of learning/tasks, and in what areas of the brain.…”